This is a Pakistan or India based IRS scam. Do not fall for it. The IRS does not initiate any legal action via phone.
Read http://www.treasury.gov/tigta/press/press_tigta-2014-03.htm
As general background information, here are a few things you can do:
1) Report it to TIGTA under http://www.treasury.gov/tigta/contact_report_scam.shtml especially if you have become a victim (lost money, gave personal information etc.). You can also file a complaint with the Federal Trade Commission at ftc.gov/complaint (include “IRS Telephone Scam" in your complaint). This way you can also help the government establish specific fraud patterns.
2) Help kill their phone lines but not by calling them back directly (the number may be spoofed and repeat calls by you may - under exceptional circumstances - amount to harassment). The scammers use Voice over IP lines (e.g. magicJack (Ymax corporation)) to make it seem as if they are calling from the US. This is always against these companys' terms of service and can lead to immediate termination of their contract and blocking of their IP addresses for future attempts to register. Do a reverse look up of their telephone number (e.g. www.whitepages.com) to identify the Voice over IP provider and report it to the company and/or law enforcement (local police and/or state attorney general)
3) If you are really annoyed: call or write to your representative in Congress. As these scams happen all over the country maybe this will trigger a reaction and provide US law enforcement agencies with the political backing and the resources they need to work in India and Pakistan together with local authorities (it can happen, read: http://m.ndtv.com/article/india/ex-call-centr ... mmission-320427). A US task force has already been set up in Jamaica to nab scammers there (see http://www.ice.gov/doclib/news/library/reports/cornerstone/cornerstone7-1.pdf). You can use the following template for your letter (more powerful!) or email:
We got a call from 202-241-1544. I had a feeling this might be a Scam because the person was very hard to understand. He said his name was Carl (Karl) Mason (I am not sure about the last name he was hard to understand.) He said he was calling for a 2013 IRS, Internal Revenue Service, Audit. He also mentioned he tried many times to contact us. (At least that is what I thought he said). We never received any prior messages. Lastly, he said something to the effect that we should not attempt to not reply to this message. After listening to the call again I think what made it hard to understand was the quality of the call and this could have been caused they are using VOIP from overseas.
'Carl Mason' was just another one of the [***] scammers, who ride through the dirt streets of Calcutta, on their camels, trying to rip off the decent people of society.